1. Field of the Invention
The present invention generally relates to a wet-type electrophotographic image forming apparatus that uses a liquid developer. More particularly, the present invention relates to a wet-type electrophotographic image forming apparatus having a system for collecting residual developer from a development unit into a developer cartridge and a method for controlling the amount of collected developer.
2. Description of the Related Art
Generally, electrophotographic image forming apparatuses can be classified as either dry-type image forming apparatuses that use a dry powder developer or wet-type image forming apparatuses that use a liquid developer. Dry-type and wet-type image forming apparatuses each have distinctive characteristics. Generally, wet-type image forming apparatuses have better print quality, with higher definition and resolution, than dry-type image forming apparatuses. As digital cameras have become more popular, the demand for color image forming apparatuses has greatly increased. They have especially increased demand for printers that produce high resolution, natural-color, prints.
To produce a desired level of print quality with a wet-type image forming apparatus, it is necessary to provide a developing unit with a larger amount of developer than the amount actually required for printing. For this reason, excess, unused developer is collected and returned to a developer cartridge. FIG. 1 schematically illustrates a conventional wet-type electrophotographic image forming apparatus that provides and collects developer.
In the apparatus shown in FIG. 1, when a user enters a printing instruction, a supply pump (not illustrated) starts to supply developer to a development unit 16 from a developer cartridge 15. When the development unit 16 is filled with developer to a certain level, the developer starts to collect naturally. That is, any excess developer returns to the developer cartridge 15 by exiting a developer outlet 17, entering into a drain 18, and flowing into the developer cartridge 15, due to gravity. While printing continues, the supply of developer by the supply pump and the natural collection of the developer occur concurrently. As a result, the development unit 16 maintains an adequate level of developer.
When printing is terminated, or, when printing stops due to an error in the middle of the printing process, a collection pump 12 is activated to collect the developer and return the developer through connection tube 13. Since the natural collection of the developer continues to take place, the developer collects into the developer cartridge 15 more rapidly. After the collection of the residual developer is completed, the collection pump 12 is stopped and, thus, the developer collection is terminated.
However, when the collection pump 12 operates, developer is returned to the developer cartridge through both drain 18 and connection tube 13. This simultaneous bi-directional inflow of the developer causes the level of developer contained within the developer cartridge 15 to increase. This increased level of developer causes air within the developer cartridge 15 to compress. The compressed air leaks out of the drain 18, creating an airflow 20 in the opposite direction of developer flow. This causes the developer to overflow and contaminate various interior parts of the electrophotographic image forming apparatus. In addition to the contamination, the overflowing developer causes malfunctions. Furthermore, the overflowing developer may leak out of the apparatus, causing severe contamination outside of the apparatus.
Accordingly, there is a need for an improved apparatus for returning excess developer in a wet-type electrophotographic image forming apparatus, and a wet-type electrophotographic image forming apparatus employing the same.